The Royal Greenwich Observatory (RGO) has a long history of involvement in timekeeping which began in 1675 when Charles II established an observatory in Greenwich Park to provide the astronomical foundations of a practical method for finding the longitude of ships at sea. The widespread acceptance of the methods developed at Greenwich led in 1884 to the adoption of the Greenwich meridian as the international zero of longitude and of mean solar time on the Greenwich meridian (OMT) as the basis of the international system of time zones. More recently the RCO has played a significant part in the development of modern timekeeping. For example, RGO worked with the National physical Laboratory in the initial evaluation of the caesium frequency in terms of an astronomical timescale, and participated in the international coordination of time signals in the early 196Os and in defining the new UTC system that was introduced in 1972. RGO has operated commercial caesium-beam clocks in-house since 1966 and has collaborated with the US Naval Observatory (USNO) in monitoring Loran-C signals for timing purposes since 1969. In the 197Os we collaborated with the US Naval Research Laboratory in time-transfer experiments using the Navigation Technology Satellites which were precursors of the Global Positioning System, but we have found it progressively more difficult to obtain staff and resources for this kind of work. These difficulties arise partly from changes in the technological basis of precise timekeeping, and partly from changes in the responsibilities of the Observatory, the objectives of its sponsoring agency and the level of funding of this agency relative to the demands now made upon it.

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